Neospora is a newly recognized toxoplasma-like protozoan that causes spontaneous abortion and/or neonatal disease in a wide range of animals. Work completed in 1993 at the california regional primate center demonstrated that nonhuman primates are susceptible to both direct fetal, and transplacental neospora infection. Transplacental infection following maternal inoculation at 43 days gestation resulted in chronic fetal encephalitis with cerebral microcavitations, and amnionitis 67-70 days post-inoculation. CNS lesions resembled the encephalitis produced in human babies with congenital toxoplasmosis. These results were published (laboratory investigation 71:236, 1994). The purpose of our current study is to determine the natural outcome of transplacental fetal infection when dams are infected at 25 and 45 days gestation using this same protocol, specifically will infected fetuses remain viable to term, and if so, do congenital cns defects develop. In 1993 2 pregnant macaques were available for study (1 infected; 1 control). The experimental animal was infected at 45 days gestation with 1.6 X 107 neospora tachyzoites. The fetus survived to term. The infant appeared normal and the neurologic exam was unremarkable; it was euthanized at age @14 days. At necropsy there was mild unilateral hydrocephalus with an associated chronic scarring multifocal encephalitis. No parasites were found in the baby's tissues although it developed a specific fetal neospora antibody titer, and neospora were isolated from fetal amniotic fluid during pregnancy. Uterine hemorrhage occurring near term in the control monkey resulted in the delivery of a dead, full-term control fetus which was otherwise unremarkable. These preliminary results indicate that fetal neosporosis in nonhuman primates can result in the development of congenital central nervous system defects, ie. Hydrocephalus. Work is in progress (8 animals divided into 2 groups infected at 25 and 45 gestational days respectively) to complete this study.